Effect of Nifekalant for Acute Conversion of Atrial Flutter: The Possible Termination Mechanism of Typical Atrial Flutter

BACKGROUND: Nifekalant is a class III antiarrhythmic drug, which is usually used for suppression of ventricular tachycardia (VT) and fibrillation. We studied the efficacy of nifekalant for acute conversion of atrial flutter (AFL) in a prospective, open label study in the intensive care unit (ICU) of cardiovascular medicine. METHODS: This study consisted of 31 patients. Twenty-six patients (84%) suffered from structural heart diseases. AFL was developed in 15 patients (48%) while on antiarrhythmic therapy with class IA or IC drugs (I-AFL group) for suppressing atrial fibrillation (AF) and in the remaining patients without such drugs (S-AFL group). Patients with prolonged QT interval, hypokalemia were excluded. All patients received one dose of 0.3 mg/kg of nifekalant over 10 minutes under continuous ambulatory monitoring. Four patients with common AFL in each group received nifekalant during electrophysiologic (EP) study. RESULTS: Nifekalant had an overall AFL conversion efficacy of 77.4% within 60 minutes. Eleven patients in S-AFL group (68.8%) and 13 patients in I-AFL group (86.7%) could be converted with mean conversion times of 10.8 +/- 6.2 and 15.0 +/- 8.0 minutes, respectively (n.s.). Conversion rate was significantly higher in patients with a short duration of arrhythmia. The two modes of AFL termination were mainly demonstrated and the preferential mode significantly differed between the two groups. One patient in each group with excessive QT prolongation (6.5%) developed torsade de pointes (TdP), requiring electrical shock in one patient (3.3%). CONCLUSIONS: Nifekalant can be used for conversion of AFL with a potent efficacy even in patients with structural heart diseases. However, caution should be required for developing TdP.